The present invention relates to an ICR ion trap comprising electrically conductive side plates of equal axial length extending in parallel to one axis, and electrically conductive end plates extending perpendicularly to the said axis, closing the space defined by the said side plates and being electrically insulated from the latter, and a voltage source serving for applying trapping potentials to the side plates and end plates.
Ion traps of this kind have been used in ICR mass spectrometers and serve the purpose of trapping the ions of substances intended to be examined by mass spectroscopy, using the cyclotron resonance. For trapping negative ions, the end plates are in this case maintained at a negative potential, relative to the side plates, while for trapping positive ions the potential of the end plates must be positive relative to that of the side plates.